Regulation of alternating circuits.



PATENTED MAY 5, 1903.

T. J JOHNSTON. REGULATION OF ALTERNATING CIRCUITS.

APPLIOATION FILED NOV. 20, 1901.

10 MODEL.

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UNITED STATES Patented May 5, 1903.

PATENT OFFICE.

THOMAS J. JOHNSTON, OF BROOKLYN, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

REGULATION OF ALTERNATING CIRCUITS.

SPECIFICATION forming part of Letters Patent NO. 726,935, dated May 5,1903. Application filed November 20, 1901. Serial No. 82,995. (Nomodel.)

To (tZZ whom it may concern..-

Be it known that I, THOMAS J. JOHNSTON, of Brooklyn, in the county ofKings and State of New York, have made certain new and usefulImprovements in the Regulation of Alternating Circuits, of which thefollowing is a specification. a

My present invention relates to the regulation of alternating circuits,and has for its 19 object to provide a convenient and efficient methodof maintaining the power factor as near to unity as is commerciallypracticable.

It is well known that the efficiency of altering -current transmissiondiminishes when current and electromotive force in the circuit are outof phase. In operation the extent to which this dephasing occurs isdependent upon the electric characteristics of the circuit in which thealternating current flows, an in- 2o crease of inductance causing thecurrent to lag and ofcapacity causingit tolead the electromotive force.It has been heretofore proposed to furnish to the circuit having'aleading or lagging current a reactance of opposite char- 2 5 acteristic,so as to correct the tendency to dephasing already referred to. The mostconvenient Way to accomplish this is by the regulation of the field of asynchronous motor. This apparatus has the characterstic of furnishingleading current when the field is strengthened above and lagging current when the strength of the field falls below what may.

be called its critical value. It is in general to this form ofregulation that my present invention is addressed; and it consistsinseparately exciting the field of a synchronous motor and furnishing tothe armature of the exciter, either by direct or inductive connection,(preferably the latter,) a current varying in value and phase with thatflowing in the main alternating circuit. The effect of this is toalter-the armature reaction of the exciter in such a way as to vary thefield magnetization of the motor to the desired extent and in thedesired direction, as will be more fully pointed out hereinafter.

Under some conditions the invention may be applied to analternating-current rotary converter, either acting alone or running inmultiple with others in a substation. Where the regulation of the systemis the principal object, it is better to employ the synchronous motor,since under some conditions if the field of the converter is lowered toomuch the continuous current from the other machines may tend to reverseits direction and drive the regulating-converter. I aim to include theuse of the converter within the scope of the claims; but, as aboveindicated, I regard the synchronous motor as the best adapted to thepractice of the invention.

Whichever form of machine may be used should have considerable iron inits fieldmagnets, so that they may not become saturated and may respondreadily and with comparative proportionality to changes in theexciting-current.

The exciter may be of any ordinary form.

It is necessary, however, that it should be operated in strictsynchronism with the mo- 7'0 tor or converter. While it is possiblewhere the exciterhas a different number of poles from the motor toaccomplish this by a suitable gearing or by operating it by a separatesynchronous motor, it is in general better, as will be apparent, to fixthe armature of the exciter upon the motor-shaft and have the samenumber of poles in the field-magnets of the two machines. Where thedevice is used merely as a regulator, which may often be founddesirable, it may be of comparatively small size and of few poles, sincemechanical difficulties under such circumstances would not prevent ahigh speed of rotation.

The polar points of the eXciter-armature should be so disposed that themaximum magnetization due to the wave of the main alternating currentwill be of opposite sign to the magnetization of the field-poles andsomewhat ahead of that due to the rotation 0 of the armature across thepoles. Under this condition if the current in the main circuit leads theelectromotive force the resultant magnetization due to thealternating-current and the eXciter-field will be cut down, and the 5current in the field of the synchronous motor will diminish, loweringits magnetization. The synchronous motor thus becomes underexcited andfurnishes an inductive reactance to the system which neutralizes theleading current. On the other hand, if the current lags the resultantmagnetization of the exciter-armature is such, inasmuch as the mag neticmaxima due to the alternating current and to the eXciter-field come morein line, as to increase the potential and current of the exciter, thusraising the effective field magnetization of the motor and. furnishing acapacity reactance which neutralizes the lagging current.

Of course the apparatus may have the ordinary regulating-resistances inthe field-circuit of the motor and also in that of the exciter, though Ihave not illustrated the latter, as its operation is well understood.

In the accompanying drawings, Figures 1 and 2 show in diagram theapplication of the invention to a synchronous motor and to a converter,the principles upon which it depends being the same in both cases.

In Fig. 1, 1, 2, and 3 are the mains of a three-phasealternating-current system which may be taken as typical of those of asystem of any desired phase relation. A is the armature of thesynchronous motor, of which E B are the fields. E is theregulating-resistance. C is the armature of the exciter, of which D isthe field. At 1* is shown a belt which of course is typical of any rigidconnection be= tween the two armatures. P P are collectorrings tappedinto the armature-winding of the eXciter at points suitably selectedaccording to the principles already outlined. To these collector-ringsis furnished from a series transformer K a current varying in characterwith that in the main circuit. In the case illustrated the mostconvenient way of obtaining the displacement of phase requisite for theoperation of the invention is to mechanically displace the armature ofthe exciter upon the shaft with reference to that of the motor.

In Fig. 2 the same reference-letters designate the same parts. A is herethe anmature of a synchronous converter supplying from the brushes a acontinuous current to the mains 4 5. There will be no difference inprinciple in the operation of the invention whether the converter be runsingly or in multiple with others; but, as already pointed out, theapplication of the invention is more limited where several convertersare used, because where the inductive reactance is made too high theconverter would tend to be driven as a continuous-current motor.

The principles upon which the invention may be operated differ from thenovel and beautiful invention described in Patent to E. W. Rice, Jr.,No. 595,412, dated December 14, 1897, although the combination of theapparatus is much the same as that therein described, because theinvention described in that patent is designed to regulate thealternating-current system by raising and lowering the potential of thegenerator as a means of regulation, thus changing its output andcompensating for the inductance drop as well as for that due toresistance by change in the terminal voltage of the generator. My

invention, on the other hand, compensates for the inductive reactance ofthe system by furnishing a balancing capacity reactance, and vice versa,substantially limiting the dephasing characteristics of the circuit. Theregulation of the generator ina system provided with my invention maythus be governed by the current-flow regardless of the power factor andbe proportioned strictly to the increase or decrease of the resistancedrop due to change in the current-flow, or at least approximately so,within commercial limits. Where an inductive connection, such as thatthrough the transformer K, is employed, regard must be had to thedifference of phase between the primary and secondary currents inselecting the desired angle of displacement of the two armatures.

Regulators varying the field of the synchronous motor by change of theresistance usually connected in series operate according to thesubdivision of the regulating-resistance into steps of greater or lessamount. The changes of the motor-field are by my invention almostmathematically incremental, and except for the slight dash-pot effect ofhysteresis (which is often desirable, inasmuch as it ohviates immediateproportionate response to momentary excessive fluctuations) nearlyinstantaneous. The desired regulation is thus more nearly accomplished,lessening the fluctuations incident to the starting and stopping ofmachinery, the variations of motor speed, and so far as it is dependentupon the characteristics of the circuit the hunting of synchronousconverters and motors.

Having thus described my invention, what I claim, and desire to protectby Letters Patent of the United States, is

1. The combination of a synchronous motor and an exciter-dynamo thearmatures of which rotate in synchronism, an electrical connectionbetween the armatures by which the alternating current passes throughthe exciterarmature, the polar points of the eXciter-armature beingdisplaced from those of the motor; whereby when the current leads, themotor furnishes a compensating inductive reactance, and when currentlags a capacity reactance, tending to correct the dephasingcharacteristics of the circuit and maintain the power factorapproximately at unity.

2. In an alternating-current system, the combination of a synchronousmotor, an exciter, and a connection between the armatures of the twomachines by which alternating current is supplied to theexciter-armature at points in its winding so selected that themagnetization caused thereby shall be somewhat in advance of that due tothe fieldmagnets of the exciter; whereby when the alternating currentleads, the exciter-field is weakened, and when the current lags, thefield is strengthened.

3. In an alternating-current system, the combination of a synchronousmotor, with means for raising or lowering its field magnetization ascurrent lags behind or leads the electromotive force in the circuit;such means consisting of an eXciter-dynamo having its armature fixed tothe shaft of the motor with its polar points displaced from those of themotor-armature, and an electric connection between the windings of thetwo armatures.

4. In an alternating-current system, means for regulating the phaserelation of current and electromotive force, consisting of a synchronousmachine, such as a motor or converter,provided with a singleregulating-winding, an exciter-dynamo furnishing the current for saidwinding, and means dependent upon the phase relation for Varying saidcurr 5 rent.

In witness whereof I have hereunto set my hand, this 12th day ofNovember, 1901, in the presence of two witnesses.

THOMAS J. JOHNSTON.

Witnesses:

ERMINA E. WALKER, DANL. J. MCNAMARA, J r.

